1. Field of the Invention
The invention relates in general to a touch control system, and more particularly, to a self-capacitive touch control apparatus for implementing multi-touch control.
2. Description of the Related Art
Operating interfaces of recent electronic products have become increasingly user-friendly and intuitive. For example, through a touch screen, a user can directly interact with applications as well as input messages/texts/patterns with fingers or a stylus, thus eliminating complications associated with other input devices such as a keyboard or buttons. In practice, a touch screen usually comprises a touch panel and a display provided at the back of the touch panel. According to a touch position on the touch panel and a currently displayed image on the display, an electronic device determines an intention of the touch to execute corresponding operations.
Existing capacitive touch sensing techniques can be roughly categorized into self-capacitive and mutual-capacitive types. Compared to mutual-capacitive touch panels, self-capacitive touch panels can be implemented through a single-layer electrode with a simpler manufacturing process and lower costs, and thus prevail in many entry-level electronic products.
FIG. 1 shows an example of a self-capacitive touch panel. In a sensing region 100, a plurality of electrodes having planar contours similar to right triangles are disposed. Each of the electrodes is connected to an upper sensor 12 or a lower sensor 14. Capacitance changes detected by the sensors 12 and 14 are transmitted to a controller (not shown) for the controller to determine a user touch position. A current controller generally calculates an x-coordinate of the user touch position in the X-direction according to the equation below:
                    x        =                                            ∑                              i                =                1                            N                        ⁢                          (                                                C                  i                                *                                  X                  i                                            )                                                          ∑                              i                =                1                            N                        ⁢                          C              i                                                          equation        ⁢                                  ⁢                  (          1          )                    
In equation (1), N represents a total number of sensors, i=1˜N, Ci represents a capacitance change detected by an ith sensor, Xi represents an x-coordinate of a center of gravity of an electrode connected the ith sensor in the X-direction.
Further, a current controller generally calculates a y-coordinate of the user touch position in the Y-direction according to the equation below:
                    y        =                              (                                                            r                  *                                      C                    U                                                  -                                  C                  D                                                            r                -                1                                      )                    *                      (                          L                              C                T                                      )                                              equation        ⁢                                  ⁢                  (          2          )                    
In equation (2), r represents a predetermined value associated with a size of the electrodes, CU represents a total capacitance change detected by all the upper sensors 12, CD represents a total capacitance change detected by all the lower sensors 14, CT is a total of CU and CD, and L represents a height of the electrodes in the Y-direction. In practice, as shown in FIG. 2, the electrodes are long and narrow trapezoids having an upper width dxs and a lower width dxl. The value r is defined as:
                    r        ≡                              dxl            +                          0.9              *              dxx                                            dxs            +                          0.9              *              dxx                                                          equation        ⁢                                  ⁢                  (          3          )                    
In equation (3), dxx represents a gap width between two neighboring electrodes.
As seen from equations (2) and (3), the controller of the capacitance touch panel generates only one set of coordinates (x, y) representing one touch position at each time point, and so the one set of coordinates (x, y) is suitable for determination of single-touch control. Limited by current self-capacitive touch sensing mechanisms, existing multi-touch control sensing can only be implemented by more costly mutual-capacitive touch control apparatuses.